The present invention relates to the sterilization arts. It finds particular application in conjunction with hydrogen peroxide vaporization systems for the sterilization of packaging containers, and will be described with particular reference thereto. It should be appreciated, however, that the invention is also applicable to other chemical vaporization systems such as peracetic acid vaporization systems.
Packaging plants, which use filling lines for filling containers with beverages, food, pharmaceuticals, and the like, are moving to aseptic processing techniques to ensure that the finished product is free of hazardous microorganisms and to maintain the shelf life of the product. As a part of the aseptic process, the containers are microbially decontaminated prior to filling. Bottles or other containers are typically decontaminated using liquid chemical antimicrobial agents, including liquid hydrogen peroxide and peracetic acid, often at elevated temperatures. An alternative approach is to blow mold the containers immediately prior to filling (known, as a blow, fill, and seal process). The concept assumes that the heat involved in the molding process will render the materials used to form the containers sterile.
Recently, hydrogen peroxide vapor has been used as a sterilant. In one method, liquid hydrogen peroxide is sprayed onto the containers. The containers are heated to convert the liquid to a vapor. In another, method hydrogen peroxide vapor is condensed on the surface of the containers to form a thin layer of liquid hydrogen peroxide. In both liquid and vapor hydrogen peroxide sterilization processes, UV radiation has been used with a view to promoting sterilization. Vaporized hydrogen peroxide is a particularly useful sterilant for these purposes because it is effective at low temperatures. Keeping the temperature of the enclosure near room temperature eliminates the potential for thermal degradation of associated equipment and items to be sterilized within the enclosure. In addition, hydrogen peroxide readily decomposes to water and oxygen, which, of course, are not harmful to the operator.
Outside of the container sterilization field, several different methods have been developed for delivering a vapor phase sterilant to an enclosure for sterilizing a load. In one option, the “deep vacuum” approach, a deep vacuum is used to pull liquid sterilant into a heated vaporizer. Once vaporized, the sterilant is propelled by its vapor pressure into an evacuated and sealed chamber. In another option, the “flow-through” approach, vaporized sterilant is mixed with a flow of carrier gas, such as air, that serves to deliver the sterilant into, through, and out of the chamber, which may be at a slightly negative or positive pressure. A solution of about 35% hydrogen peroxide in water is injected into the vaporizer as fine droplets or mist through injection nozzles. The droplets fall on a heated surface which heats the droplets to form the vapor, without breaking it down to water and oxygen. A heated carrier gas is often used to ensure that the heat transfer surface remains at or above the boiling temperature of the hydrogen peroxide.
Trace amounts of hydrogen peroxide on food packaging can affect the flavor of the product or result in other undesirable changes, such as a change in the color of the product. Food packaging regulations now limit hydrogen peroxide residues on containers to a maximum of 0.5 ppm in the United States. Liquid hydrogen peroxide sterilization and condensed vapor sterilization systems are currently unable to meet these stringent regulations without extensive post sterilization processing. For example, rinsing has been used in an attempt to remove the hydrogen peroxide residues. However, unless a high purity water supply can be assured, which tends to be costly, recontamination of the sterilized containers is likely to occur. Heat, for example a 400° C. drying phase, has also been used to attempt to reduce the residual level, but adds considerably to processing time and cost and cannot generally be used with thin-walled plastic bottles.
Additionally, current vaporization systems are unable to handle the latest, high speed bottling plants. With bottles being processed and filled at rates of up to 1000 bottles per minute, or more, it is desirable to have a sterilization system that can supply sterilized bottles at a sufficient rate to meet this demand. The capacity of current drip-feed vaporizers is limited because the carrier gas flow and vaporization step tend to reduce the temperature of the heated plate.
One solution has been to increase the size of the vaporizer and the injection rate of hydrogen peroxide into the vaporizer. Another solution is to employ a multiple firing vaporizer, in which different areas of a vaporizer plate are sequentially supplied with the hydrogen peroxide solution Although helpful, the larger vaporizer still suffers from concentration variations and condensation concerns.
Yet another solution is to use multiple vaporizers to feed a single enclosure. The vaporizers may each be controlled independently, to allow for variations in chamber characteristics. However, the use of multiple vaporizers adds to the cost of the system and requires careful monitoring to ensure that each vaporizer is performing efficiently.
The present invention provides a new and improved vaporization system and method which overcomes the above-referenced problems and others.